EBMUD officials initially said seven water pipes broke following the earthquake at 6:49 a.m. Monday, but have since clarified that two others also ruptured.
The pipes, which include mains and service lines, were cast-iron pipes that are more susceptible to ground movement from earthquakes, EBMUD spokeswoman Tracie Morales-Noisy said.
Of the nine that broke, five were in Oakland near the epicenter of the quake, while the other four were in areas like Berkeley and Richmond, Morales-Noisy said.
Seven of the pipes were repaired Monday and overnight, while the other two were lower-priority lines that will be fixed today, she said.
The average age of cast-iron pipes in the EBMUD system is about 80 years old, with some pipes dating as far back as the 1880s, Morales-Noisy said.
She said the incident serves as a reminder of the infrastructure hazards of a major seismic event like the Loma Prieta earthquake of 1989.
"We could see hundreds or thousands of main breaks, and it would have an enormous impact," Morales-Noisy said. "We recommend that customers have a minimum of three to seven days worth of water in their home in the event of a major water emergency."
She advised residents to keep at least one to two gallons of water per day for each person in the home.
"It doesn't have to be a major emergency, it could be just a main break," Morales-Noisy said. "Things are unpredictable, and you never know when you'll need a water supply."
The Napa quake was the largest temblor to hit the San Francisco Bay Area since the magnitude-6.9 Loma Prieta earthquake in 1989 on the San Andreas Fault.
The California Emergency Management Agency is reminding people statewide to be ready for any type of natural disaster.
We're all encouraged to have emergency kits stocked with items including:
Click here to check out Prepare NorCal's guidelines for stocking your emergency kit and developing an emergency plan for your family.